Ionization-crack fluid analyzer



June 7, 1966 G. F. VANDERSCHMIDT 3,

IONIZATION-GRACK FLUID ANALYZER Filed Dec. 28, 1962 SPACING (CITL) INVENTOR.

BY Maw! GEORGE FREDERICK VANDER SCHMIDT SOURCES GAS FLOW ATTORNEYS 3,255,348 IONIZATION-CRACK FLUID ANALYZER George Frederick Vanderschmidt, Boston, Mass., assignor to Lion Research Corporation, Cambridge, Mass., a corporation of Massachusetts Filed Dec. 28, 1962, Ser. No. 247,957 Claims. (Cl. 250--43.5)

The present invention relates to methods of and apparatus for the radiological analysis of gases and other fluid media, being particularly directed to an improved radiological gas analyzer.

As is explained in my copending application, Serial No. 94,786, filed March 10, 1961 now Patent No. 3,174,035 for Method of and Apparatus for the Radiological Analysis of Gases and the Like, the art has struggled over the years with the problem of detecting small traces of gas or other fluid constituents in a fluid sample. Numerous ionization chambers have been proposed, including various types of electrode configurations, but the problem of providing a high signal-to-noise ratio in the detection of faint traces of impurities or other constituents has been diflicult to solve. A very satisfactory solution of this problem for certain applications, however, is presented in my said copending application wherein, unlike prior art cross-section detectors, the ionization-current-detecting electrode is positioned in a region of the ionization chamber where the energy of the radiation particles emitted into the ionization space has become substantially completely absorbed in the gas within the space. A substantial number of particles then do not impinge upon the ionization-current-collecting electrode, improving signal-to-noise ratios.

Another approach to the solution of this problem that is more particularly suited to gas mixtures and the like involving constituents that are of considerably different cross-section, is represented by the present application,

wherein an unexpected discovery has been made of phenomena immediately adjacent one of the ionization chamber electrodes upon which a radioactive source is pro-' vided. In accordance with this discovery, vastly improved signal-to-noise ratio has been obtained by limiting the space between the ionization chamber electrodes to sub stantially a crack, as distinguished from the entirely opposite approach employed in prior-art apparatus of this character.

A further object of the invention is to provide a new and improved method of fluid-ionization analysis and a novel analyzer of more general utility, as well.

Additional objects will be explained hereinafter and will be more particularly pointed out in connection with the appended claims.

The invention will now be described in connection with the accompanying drawings, FIG. 1 of which is a schematic flow-and-circuit diagram illustrating an improved application of the invention;

FIG. 2 is a partial longitudinal section of preferred ionization chamber suitable for use in the system of FIG. 1;

FIG. 3 is an experimentally obtained graph illustrating the preferred region of operation of the invention; and

FIG. 4 is a perspective view, partly in section, illus trating a modification.

Referring to FIG. 1, a fluid medium, such as a ga mixture, is applied at 8 to each of a pair of filter systems United States Patent 3,255,348 Patented June 7, 1 966 ice 1 a fluidthat is similar to that at the output 2 of thefilter system 2, except that one or more fluid constituents has or have been filtered out. As an illustration, the incoming fluid mixture at 8 may comprise oxygen with traces of carbon dioxide, the proportion of the latter being the subject matter of the desired measurement. Each of the filter systems 1 and 2 may be provided with anhydrous calcium sulfate or some similar dehydrating agent to remove water vapor from the incoming fluid mixture, and the filter system 1 may further be provided with, for example, a mixture of asbestos and sodium hydroxide (Ascarite) or any other well-known similar substance for absorbing and filtering out the carbon dioxide. Thus the fluid channel 2' will contain both the oxygen and carbon dioxide, while the fluid channel 1' will contain only the oxygen; with the two channels preferably maintained at the same pressure through this common feeding arrangement, such as at a pressure of the order of a few pounds per square inch in a space capsule, or at some other pressure generally, though not essentially, different from atmospheric pressure. The fluid flow continues along channels 1' and 2 to respec tive, preferably similar, ionization chambers 3 and 4 and thence out of the chambers 3 and 4, as at 3' and 4, to a common outlet 8'.

The construction of the ionization chambers 3 and 4 in the path of the fluid channels 1' and 2 is desirably the same so that it will suflice, as an illustration, to describe only the chamber 4, the details of a preferred form of which are contained in FIG. 2.

The fluid inlet conduit 2' of FIG. 2 is substantially axially disposed in the right-hand end section of a cylindrical chamber housing 4, the left-hand end section of which is provided with an axially alined outlet conduit 4'. Mounted within the housing 4 is a first conductive electrode member I, illustrated in the form of a solid cylindrical conductor axially mounted within the housing 4 by corner insulator rings 10. Near opposite ends of the conductive electrode cylinder I, axial channels 2" and 4" are provided which respectively communicatewith the inlet 2 and the outlet 4' and with internal radial channels 2" and'4 that permit the fluid medium to pass along the outer circumferential surface of the electrode I in the direction of the arrows.

The electrode I is provided with a radioactive layer 12 of predetermined area extending along the principal outer cylindrical surface area of the electrode I. For reasons later evident, the radioactive layer 12 is preferably a low-energy, high-intensity B-ray emitter with at least a few months half-life in order to provide utility for the device, and preferably void of -ray emissions. Among the most desirable radioactive sources of this character are tritium bound as a hydride in a conductive layer of titanium, zirconium, yttrium or hafnium. More generally, the radioactive layer 12 may be bound in a conductive layer selected from the group consisting of the transition, rare-earth, alkali and alkaline-earth metals (Progress in Metal Physics, Bruce Chalmers, Interscience Publishers, Inc., 1953, pp. 112-113, etc.)

Closely juxtaposed to the outer cylindrical surface of.

the electrode I and its radioactive layer 12 is a second electrode II, shown in the form. of a substantially parallel concentric conductive cylinder, the inner surface of which covers, substantially coextensively, the predetermined area of the radioactive layer 12 with a mere crack 11 separating the electrodes I and II: The electrode II is mounted by insulating rings The fluid medium is caused to flow longitudinally through or along the crack 11 between the electrodes I and II.

As before stated, it has been discovered that with this kind of construction, vastly improved signal-to-noise ratios in the detection of ionization produced in the fluid medium passing through the crack 11 are attained. While it is not necessary to offer theories for this surprising result, it being suflicient to describe the arrangement that has been found to produce the same in practice, the following may serve as a possible explanation of these improved results. Through the use of a substantial area of radioactive surface, a broadening or integrating of the radiation intensity within the space 11 is achieved, as distinguished from peak regional radiation effects that occur with radioactive sources of limited dimensions. Otherwise stated, the construction permits the use of almost unlimited amounts of ionizing radiation while, at the same time, retaining the sensitivity gained by the use of the narrow crack spacing I1. Within this narrow spacing 11, the lowenergy high-intensity B-rays will produce suflicient ionization of the larger cross-section molecules, while producing much less ionization of the smaller crosssection molecules; so that a very marked difference in the ionization effect upon the larger cross-section molecules is available right near the surface of the radioactive layer 12. As one gets further and further from this surface 12, the difference in ionization effect upon the larger and smaller cross-section molecules becomes smaller and smaller.

Referring, for example, to FIG. 3, the width or spacing of the crack 11 is plotted in centimeters (logarithmically) along the abscissa; whereas the relative sensitivity, ascertainable through measurement of the ionization current in the later-described output circuit, is plotted along the ordinate, the relative sensitivity being a measure of the signal-to-noise ratio. This experimental result was obtained for a chamber 4 operating with oxygen and carbon dioxide mixtures at about atmospheric pressure, with a tritium-titanium foil layer 12 extending as a cylindrical electrode I about 1 /2 long with a cylindrical diameter of about 1". The reason for the utilization of low-energy fi-rays resides in the fact that it is desired to prevent the production of X-rays upon the striking of the closely spaced second electrode II, and for radiation safety purposes. The width of the crack or narrow spacing 11 was varied from several centimeters down to the order of tenths of a millimeter. It was found that the degree of ionization of the carbon dioxide larger-cross-section molecules could be detected with vastly increased signal-tonoise ratio as the width of the crack 11 was made smaller, as particularly indicated by the greater sensitivity at the region III of FIG. 3. The small volume of the crack 11 is also useful because it speeds up the speed of response and reduces the level of the polarizing voltage necessary to cause the ionization chamber III to operate with saturation; in fact, with a crack space of only 5 volts are required to operate the ionization chamber.

Referring back to FIG. 1, therefore, the output ionization-current-detecting circuit may be traced by conductor 13 from electrode I, through a polarizing voltage source 6, sufficiently large to produce saturation of the chamber (of the order of 200 volts in the above-described tests), thence through a meter or other indicator '7, and by conductor 13' to the other electrode II. The conductors 13 and 13' are shown in FIG. 2 extending through insulating terminal seals 14 and 14 in the housing chamber 4. The meter or indicator 7 provides a measure of the ionization current and, in the differential circuit of FIG. 1, wherein the meter 7 is also connected in the output of the ionization chamber 3, with its oppositely poled voltage source 5, enables a difference or comparison measurement that indicates the amount of carbon dioxide in the fluid mixture at 8.

In order to enable slight variations in spacing 11, as when, for example, different gas pressures are employed at 8, a structure similar to that illustrated in FIG. 4 may be employed. The outer electrode II is also provided with an internal radioactive layer 12' separated from the radioactive layer 12 on the electrode I by the space 11. Tightening of the adjustable screws 15 enables slight variations in the width of the crack or space 11.

While the invention has been described in connection with the system and circuit of FIG. 1, it will be evident that the novel ionization chamber of FIG. 2 may also be used with a wide variety of other systems whenever the novel results obtainable therewith are sought. The polarity of the output circuit of FIG. 1 may be reversed, if desired. Other types of electrode configurations may also be employed, though the described parallel or concentric cylindrical structure is preferred. The filter systems 1 and 2, moreover, may actually be connected to the inlet of the ionization chambers within the chambers, if desired. Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An ionization-crack fluid-analyzer having, in combination, a first electrode provided with a surface of predetermined area containing a radioactive layer, a second electrode provided with a surface substantially coextensive with the said predetermined area, the second electrode being juxtaposed to the first electrode with a crack therebetween, means for passing fluid through the crack between the electrodes, means for applying a voltage between the electrodes, indicator means for measuring the current produced between the electrodes, and means for varying the width of the said crack.

2. An ionization-crack fluid-analyzer having, in combination, a first electrode provided with a surface of predetermined area containing a radioactive layer, a second electrode provided with a surface substantially coextensive with the said predetermined area, the second electrode being juxtaposed to the first electrode with a crack therebetween, means for passing fluid through the crack between the electrodes, means for applying a voltage between the electrodes, and indicator means for measuring the current produced between the electrodes, the said electrodes being substantially parallel.

3. An ionization-crack fluid-analyzer having, in combination, a pair of fluid channels for passing fluids that differ in the presence of a predetermined fluid constituent, a pair of ionization chambers, one corresponding to and connected with each channel, and each comprising a first electrode provided with a surface of predetermined area containing a radioactive layer, a second electrode provided with a surface substantially coextensive with the said predetermined area and juxtaposed to the first electrode with a crack therebetween, means for passing fluid from each channel through the crack between the electrodes of the corresponding ionization chamber, means for applying voltage between the electrodes of the chambers, and means for measuring the current produced between the electrodes of each chamber, thereby to enable a comparison of the ionization effect produced in the fluid, with and without the said fluid constituent.

4. An analyzer as claimed in claim 3 and in which means is provided .in one of the channels for filtering out the said predetermined fluid constituent.

5. An analyzer as claimed in claim 3 and in which means is provided for maintaining the fluid flow in the said channels and chambers at substantially the same pressure.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Dunmore 324-33 Roehrig 250-83.6

Strange 25043.5

Zito 25043.S

Wilson 2s0-43.s

6 OTHER REFERENCES 5 December 1956, pages 1958 to 1963.

RALPH G. NILSON, Pi imary Examiner.

J. W. LAWRENCE, FREDERICK M. STRADER,

I Examiners. 

1. AN IONIZATION-CRACK FLUID-ANALYZER HAVING, IN COMBINATION, A FIRST ELECTRODE PROVIDED WITH A SURFACE OF PREDETERMINED AREA CONTAINING A RADIOACTIVE LAYER, A SECOND ELECTRODE PROVIDED WITH A SURFACE SUBSTANTIALLY COEXTENSIVE WITH THE SAID PREDETERMINED AREA, THE SECOND ELECTRODE BEING JUXTAPOSED TO THE FIRST ELECTRODE WITH A CRACK THEREBETWEEN, MEANS FOR PASSING FLUID THROUGH THE CRACK BETWEEN THE ELECTRODES, MEANS FOR APPLYING A VOLTAGE BETWEEN THE ELECTRODES, INDICATOR MEANS FOR MEASURING THE CURRENT PRODUCED BETWEEN THE ELECTRODES, AND MEANS FOR VARYING THE WIDTH OF THE SAID CRACK. 